myxce/.kiro/specs/scheduler-sim-repl-verbosity/design.md

Design Document

Overview

Purpose: This feature reduces and reorganizes the console output the xce_scheduler --interactive simulation REPL prints while executing continue, so an operator can watch a long replay's progress without wading through repetitive, low-information lines.

Users: XCE scheduler engineers and operators debugging scheduling behavior via xce_scheduler -i -s <replay>, a capability shipped by the scheduler-core spec.

Impact: Changes the text xce_repl_on_event() (repl_break.c) and sim_print_decision() (sim_loop.c) print while sim->repl_state->mode == XCE_REPL_MODE_CONTINUE; the REPL's command prompt string (repl_command_loop(), repl.c); info worker's/info resource's resource-value rendering and the set command (repl_info.c, repl_params.c); and help's listing plus break's unrecognized-event-type error text (repl.c, repl_break.c). No change to scheduling decisions, replay determinism, or step mode's per-event/per-decision detail; every other aspect of every REPL command's parsing and behavior is unchanged.

Goals

• Suppress routine per-event echo during continue execution, while still surfacing structural changes (Requirement 1).
• Replace unconditional per-decision echo with one summary line per round during continue (Requirement 2).
• Collapse consecutive idle or unchanged rounds into a single range notification (Requirement 3).
• Compress array-job identifier lists into index ranges everywhere the REPL displays multiple job identifiers together, including info worker's assigned-job listing (Requirement 4).
• Leave step mode's per-event/per-decision detail, and every other aspect of the REPL's existing commands, unchanged except where this feature's own requirements explicitly say otherwise (Requirement 5).
• Show the current session and timestamp in the REPL's command prompt, in both step and continue modes (Requirement 5.5).
• Render byte/megabyte-denominated resource values in a human-readable unit under operator control (set units), and lay out info worker's/info resource's listings as a grouped table (Requirement 6).
• Reorganize help's command listing into labeled, consistently-aligned sections, and make break's valid event types discoverable in both help and its error message (Requirement 7).

Non-Goals

• New REPL commands or newly inspectable data (limit usage, pend-reason detail) — tracked separately under the scheduler-sim-diagnostics brief.
• Any change to scheduling/allocation logic or to the deterministic outcome of a replay.
• Non-interactive (headless, no -i) scheduler output.
• Resolving bug-1611 (whether DISPATCH decisions are structurally invisible in replay mode) — this spec only guarantees Requirement 2.4 holds regardless of that investigation's outcome (see Design Decisions, research.md).
• Unit-aware formatting for any resource outside the confirmed canonical-bytes list (mem, tmp, maxmem, maxtmp, maxswap) and the confirmed canonical-megabytes swp — xce_resource_t (src/include/xce/types.h) carries no units metadata at all, so an arbitrary operator-defined or plugin resource is displayed as a plain unitless number, exactly as today.

Boundary Commitments

This Spec Owns

• Console output formatting/verbosity logic inside xce_repl_on_event() (repl_break.c), the continue-mode gate on sim_print_decision()'s call site (sim_loop.c), and the new round-boundary rollup/collapse logic added at xce_repl_post_session_check() (repl.c).
• The new jobid-range-compression helper and every call site that adopts it, including info worker's assigned-job listing (repl_info.c).
• New xce_sched_repl_state_s fields required to track collapse state across rounds.
• The REPL prompt string construction in repl_command_loop() (repl.c).
• Resource-value unit classification/scaling helpers, the units_mode display setting, and the table/grouping layout of info worker's and info resource's resource listings (repl_info.c, repl_params.c).
• repl_print_help()'s listing structure (repl.c) and repl_cmd_break()'s unrecognized-event-type error text (repl_break.c).

Out of Boundary

• Any new info/break/set top-level subcommand or newly inspectable scheduler data (set units is a new option of the existing set command, not a new command).
• Scheduling/allocation/decision logic itself (scheduler.c, src/plugins/).
• sim_print_decision()'s behavior when sim->interactive is false (headless mode) — unchanged.
• Root-causing bug-1611 — a separate investigation; this spec only ensures its own requirements hold regardless of the answer.
• Unit-aware formatting for resources outside the confirmed bytes/megabytes list (see Non-Goals) — no generic units-metadata system is added to xce_resource_t or the wire protocol.

Allowed Dependencies

• Existing xce_sched_repl_state_s fields (mode, last_n_dispatch/last_n_pend/last_n_preempt, session_count) — repl_internal.h.
• The existing core->jobs iteration idiom (iter_make/iter_next, JOB_IS_PEND) already used by repl_info_jobs().
• Existing helpers fmt_jobid_ex() (lib/utils.c) and repl_format_ts_human() (repl.c).
• Must not add a new call site to sim_loop.c's main loop beyond gating the two calls that already exist there (sim_print_decision, the xce_repl_check_event wrapper) — that file is documented at its line-budget ceiling (repl.h's own header comment).
• xce_sched_repl_state_s.session_count and xce_core_now()/repl_format_ts_human() (repl.c) for the prompt's session/timestamp content — no new state needed for that part.
• repl_break.c's existing BP_KIND_TABLE (currently static/file-local) — exposed via one new shared accessor declared in repl_internal.h, rather than duplicated as a second hardcoded list, so help and the unrecognized-event-type error can never drift out of sync with each other or with the table itself.
• The existing repl_command_loop() call site's readline(XCE_REPL_PROMPT) (repl.c:439) — this feature makes the prompt argument dynamic in place; no new call site.
• src/controller/testsuite/test.c's is_bytes_valued_resource()/format_bytes_human() as a design precedent only (same classification list, same adaptive B/KB/MB/GB/TB/PB algorithm) — not a shared symbol, since xce_test and xce_scheduler are separate binaries; the scheduler gets its own repl_*-named port of the same logic.

Revalidation Triggers

• If scheduler-sim-diagnostics adds pend-reason data, the round-rollup collapse fingerprint (Design Decisions, research.md) may need to incorporate it — revisit Requirement 3.2's implementation then.
• If bug-1611 is confirmed a real dispatch-visibility gap and separately fixed, the rollup's dispatch count source should switch from the decision tally to the same state-derived approach already used for the pend-jobid set.
• Any change to xce_sched_repl_state_s's existing mode/tally fields by another spec should re-check this feature's rollup logic.
• If a future spec adds real units metadata to xce_resource_t (see Non-Goals), the hardcoded bytes/megabytes classification lists added here should be replaced by reading that metadata instead of the name-match lists.
• If repl_break.c's BP_KIND_TABLE gains or loses an entry (e.g. a new breakpoint-able event type), help and break's error message pick it up automatically via the shared accessor — no separate list to update, by construction.

Architecture

Existing Architecture Analysis

• repl.c/repl_break.c/repl_info.c/repl_params.c form the REPL command family under scheduler-core. repl.h folds the sim->interactive gate into static inline wrapper functions so sim_loop.c's own diff stays to single-line, brace-free call expressions — this feature's sim_loop.c change must follow that same convention rather than adding a bare if block to the loop body.
• xce_sched_repl_state_s (repl_internal.h) is the REPL's own session-scoped state struct, zero-initialized via calloc in repl_state_ensure() — new fields need no separate lifecycle.
• xce_repl_post_session_check() (repl.c) already runs exactly once per completed round, immediately after that round's decisions are drained, purely to check the step-budget pause condition today.

Architecture Pattern & Boundary Map

Correction (post-review): breakpoint-hit detection and structural-event classification both live in repl_break.c (xce_repl_on_event, xce_repl_on_begin_round, xce_repl_on_decision — each calls repl_command_loop() directly on a match), not in repl.c. Requirement 3.5 ("a structural event ends the active range") and Requirement 3.6 ("a breakpoint hit ends the active range") therefore cannot be satisfied by round-boundary logic in repl.c alone — repl_break.c needs a way to force-flush the Round Rollup's active range from its own call sites. The Round Rollup component now exposes an explicit flush entry point for this, called from both files.

flowchart TD
    RoundEnd[Round decisions drained] --> Query[Query core jobs for PEND state]
    Query --> Fingerprint[Build fingerprint: dispatch count, pend jobid set, preempt count]
    Fingerprint --> Compare{Matches active collapsed range}
    Compare -->|Yes| Extend[Extend active range silently]
    Compare -->|No| FlushCall[Call round rollup flush]
    FlushCall --> Begin[Begin new collapsed range with this round]
    Extend --> NextRound[Advance to next round]
    Begin --> NextRound
    StructuralEvent[Structural event classified in repl_break.c] --> FlushCall
    BreakpointHit[Breakpoint hit detected in repl_break.c] --> FlushCall
    ReplayComplete[Replay completion in repl.c] --> FlushCall
    FlushCall --> PrintRange[Print the flushed range, if one was open]

Architecture Integration:

• Selected pattern: a state accumulator attached to the existing round-boundary hook (xce_repl_post_session_check), exposing one shared flush entry point that repl_break.c's event/breakpoint/decision hooks and repl.c's replay-completion hook all call — no new hook call sites added to sim_loop.c.
• Domain/feature boundaries: the Round Rollup's state and flush/print logic live in repl.c; repl_break.c calls the flush entry point but does not own or mutate the collapse state directly; sim_loop.c only gains a mode gate on its two existing calls.
• Existing patterns preserved: repl.h's sim->interactive-gated inline-wrapper convention; repl.c's shared-helper convention (repl_format_ts_human, repl_split_tokens) extended with two new shared helpers (range compression, and the round-rollup flush entry point declared in repl_internal.h for repl_break.c to call).
• New components rationale: deciding "print now vs. extend silently" requires comparing against the previous round's fingerprint, which must persist across separate xce_repl_post_session_check() invocations — hence new persistent fields on xce_sched_repl_state_s rather than function-local state. The flush entry point exists because three independent call sites (round boundary, breakpoint hit, replay completion) across two files all need to end an active range the same way.
• Steering compliance: one domain per file preserved; no new production .c file needed; snake_case/repl_* naming conventions followed throughout.

Technology Stack

Layer	Choice / Version	Role in Feature	Notes
Scheduler daemon (C, gnu17)	existing src/scheduler/ toolchain, no new dependency	All logic lives in existing REPL/sim-driver translation units	Matches tech.md; no new library, no CGO/Go involvement

File Structure Plan

Modified Files

• src/scheduler/src/repl_internal.h — extend xce_sched_repl_state_s with round-collapse state fields (see Data Models), a new units_mode field (Requirement 6), and declare the new shared jobid-range-compression helper, resource-formatting helpers, and the BP_KIND_TABLE accessor (Requirement 7).
• src/scheduler/src/repl_break.c — xce_repl_on_event() gains routine-vs-structural event classification gated on rs->mode (Requirement 1); repl_print_event_summary()'s JOB_PUSH-style cases adopt the jobid-range-compression helper (Requirement 4); xce_repl_on_event(), xce_repl_on_begin_round(), and xce_repl_on_decision() each call the Round Rollup's flush entry point before printing a structural-event line or before re-entering repl_command_loop() on a breakpoint hit (Requirement 3.5, 3.6); repl_cmd_break()'s unrecognized-event-type error gains the full valid-event-type listing, rendered via a new shared accessor over the existing BP_KIND_TABLE (Requirement 7.5); repl_cmd_delete() already fixed independently (bug-1761, strtol+endptr validation) — no further change needed here for this spec.
• src/scheduler/src/repl.c — xce_repl_post_session_check() gains the round-boundary fingerprint/collapse logic (Requirements 2, 3); implements the new shared jobid-range-compression helper (Requirement 4) and the Round Rollup's flush entry point (Requirement 3.5, 3.6), following the file's existing shared-helper convention; xce_repl_on_replay_complete() calls the same flush entry point before printing the existing replay-complete banner; repl_command_loop()'s readline(XCE_REPL_PROMPT) call gains a per-iteration dynamically-built prompt (Requirement 5.5); repl_print_help() is rewritten into labeled, consistently-aligned sections, info config moves next to the other info lines, and the break line grows the same BP_KIND_TABLE-derived event-type listing repl_break.c's error message uses (Requirement 7).
• src/scheduler/src/repl_info.c — new resource-value classification/scaling helpers (byte-denominated list, swp's megabyte special case, whole-number formatting) and a table/grouping rewrite of repl_info_worker()'s and repl_info_resource()'s resource-listing loops, both reading rs->units_mode (Requirement 6); the assigned-job listing in repl_info_worker() adopts the jobid-range-compression helper (Requirement 4.5).
• src/scheduler/src/repl_params.c — repl_cmd_set() gains a units raw|human|both branch alongside the existing speed/output/verify branches, storing the selection on the new rs->units_mode field (Requirement 6.2, 6.3).
• src/scheduler/src/sim_loop.c — the existing call site invoking sim_print_decision() gains a continue-mode gate, mirroring repl.h's inline-wrapper convention (Requirements 2, 5).
• src/scheduler/include/repl.h — no functional change expected; existing inline wrappers already cover the gating points this feature needs.

New/Modified Test Files

Correction (post-review, task 2.1): test_repl_execution_control.c was already over this project's 800-line cap (937 lines) before this feature's work began. Landing task 2.1's Round Rollup tests there per the original plan below pushed it to 1563 lines — nearly double the cap, and past the ~1000-line threshold this exact spec family already treats as a split trigger (test_repl_snapshot_params.c was split out of test_repl_breakpoints_inspection.c for precisely this reason; see that file's own meson.build comment). Round Rollup's tests (task 2.1, and any Round-Rollup-internal portion of later tasks, e.g. Requirement 3.5's flush-on-structural-event/breakpoint interaction) now live in a new src/scheduler/testsuite/test_repl_round_rollup.c instead, duplicating (not sharing) whatever pre-existing static fixture helpers it needs — the established convention this same file pair (test_repl_breakpoints_inspection.c/test_repl_snapshot_params.c) already follows, rather than factoring out a shared test-helper header. test_repl_execution_control.c remains the target for Requirement 1's Event Echo Gate tests, the sim_print_decision gate tests, the Requirement 5 no-regression checks, the new prompt-content tests (Requirement 5.5), and help-listing structure tests (Requirement 7.1-7.4) — but re-check its line count before landing each of those; if it approaches the cap again, split further rather than growing past it.

• src/scheduler/testsuite/test_repl_execution_control.c — child-process output-capture tests covering Requirement 1, the Requirement 5 no-regression checks (this file already drives sched_sim_driver_run() end-to-end and captures real process output via child_continue_then_inspect-style helpers); also gains the new prompt-content tests (Requirement 5.5) and help-listing structure tests (Requirement 7.1-7.4) — the natural home given it already exercises readline()/prompt-adjacent behavior and no help test exists anywhere today.
• src/scheduler/testsuite/test_repl_round_rollup.c (new, per the Correction above) — child-process output-capture tests for Requirements 2 and 3 (per-round decision summary, collapsing, the shared flush entry point, and its call from xce_repl_on_replay_complete).
• src/scheduler/testsuite/test_repl_output_compression.c (new) — focused unit tests for the jobid-range-compression helper (Requirement 4): a pure function, tested without the process harness.
• src/scheduler/testsuite/test_repl_resource_formatting.c (new) — focused unit tests for the byte/megabyte classification and adaptive human-scaling helpers (Requirement 6.1, 6.2, 6.5): pure functions, tested without the process harness, mirroring test_repl_output_compression.c's pattern.
• src/scheduler/testsuite/test_repl_breakpoints_inspection.c — extended with info worker/info resource table-layout and units-mode-display tests (Requirement 6.6, alongside its existing info worker/info resource tests) and break's enriched unrecognized-event-type error test (Requirement 7.5, alongside the existing test_break_unrecognized_event_type_rejected).
• src/scheduler/testsuite/test_repl_snapshot_params.c — extended with set units raw|human|both parsing/validation tests (Requirement 6.2, 6.3), alongside its existing set speed/set output/set verify tests.

System Flows

See the Architecture Pattern & Boundary Map diagram above — it is the only non-trivial flow this feature introduces (a per-round branching decision with two exit points: silent extension, or flush-and-restart). Per-event classification (Requirement 1) is a simple, non-branching gate and does not warrant a separate diagram. The three later-added components (REPL Prompt Context, Resource Value Formatter, Help & Breakpoint Discoverability) are likewise simple, single-purpose lookups/formatters with no multi-step state machine of their own — a name-list check, an adaptive-unit loop, and a table lookup, respectively — so none of them warrant a separate diagram either.

Requirements Traceability

Requirement	Summary	Components	Interfaces	Flows
1.1, 1.2, 1.3, 1.4	Mode-aware event echo	Event Echo Gate	xce_repl_on_event	n/a (per-event, upstream of round boundary)
2.1, 2.2, 2.3, 2.4	Per-round decision summary	Round Rollup	xce_repl_post_session_check, state-derived pend query	Round-boundary flow
3.1, 3.2, 3.3, 3.4	Collapsing repetitive rounds (idle/unchanged detection, range content)	Round Rollup (collapse state)	fingerprint compare / flush	Round-boundary flow
3.5, 3.6	Ending an active collapsed range on outcome change, structural event, breakpoint hit, or replay completion	Round Rollup (flush entry point, and its own call from xce_repl_on_replay_complete), Event Echo Gate (calls it on structural events/breakpoint hits)	repl_round_collapse_flush	Round-boundary flow
4.1, 4.2, 4.3, 4.4, 4.5	Job identifier range compression	Jobid Range Compressor	repl_fmt_jobid_range	n/a (pure formatting)
5.1, 5.2, 5.3, 5.4	No regression to step mode / other commands, outside this feature's explicit exceptions	Event Echo Gate, sim_print_decision gate	mode checks	n/a
5.5	REPL prompt shows session/timestamp	REPL Prompt Context	repl_build_prompt	n/a (per-iteration, upstream of dispatch)
6.1, 6.2, 6.3, 6.4, 6.5	Human-readable resource value formatting, set units option	Resource Value Formatter	repl_is_bytes_valued_resource, repl_format_bytes_human, repl_cmd_set's units branch	n/a (pure formatting + state)
6.6	info worker/info resource table/grouping layout	Resource Value Formatter	repl_info_worker, repl_info_resource	n/a (rendering only)
7.1, 7.2, 7.3	help listing reorganized into labeled, aligned sections	Help & Breakpoint Discoverability	repl_print_help	n/a (rendering only)
7.4, 7.5, 7.6	break event types discoverable in help and its error message; no other command's existence, parsing, or output changes	Help & Breakpoint Discoverability	repl_bp_kind_names (shared accessor over BP_KIND_TABLE)	n/a (pure formatting)

Components and Interfaces

Component	Domain/Layer	Intent	Req Coverage	Key Dependencies (P0/P1)	Contracts
Event Echo Gate	REPL / repl_break.c	Classify each event as routine or structural and gate the per-event echo by mode	1.1-1.4	rs->mode (P0), Round Rollup flush entry point (P0)	State
Round Rollup	REPL / repl.c	Build a per-round fingerprint, print it, or extend/flush a collapsed range; expose a flush entry point callable from breakpoint/structural-event/replay-complete sites	2.1-2.4, 3.1-3.6	core->jobs query (P0), existing decision tally (P0)	State, Service
Jobid Range Compressor	REPL / repl.c (shared helper)	Compress array-job identifier lists into index ranges	4.1-4.5	fmt_jobid_ex decomposition (P0)	Service
sim_print_decision gate	Sim driver / sim_loop.c	Suppress the direct per-decision print when the Round Rollup will report it instead	2.3, 5.1	REPL mode state (P0)	State
REPL Prompt Context	REPL / repl.c	Build the readline() prompt string from the current session and timestamp, falling back to the plain prompt before any session begins	5.5	rs->session_count (P0), xce_core_now/repl_format_ts_human (P0)	Service
Resource Value Formatter	REPL / repl_info.c, repl_params.c	Classify a resource's canonical wire unit (bytes/megabytes/unitless), render it per the operator's units_mode, and lay out info worker/info resource's listings as a grouped table	6.1-6.6	is_bytes_valued_resource/format_bytes_human (test.c) as design precedent (P0), rs->units_mode (P0)	Service, State
Help & Breakpoint Discoverability	REPL / repl.c, repl_break.c	Group and align help's listing, and expose BP_KIND_TABLE's full valid-event-type set to both help and break's error message via one shared accessor	7.1-7.6	BP_KIND_TABLE (P0)	Service

REPL Output (repl.c / repl_break.c / repl_info.c / repl_params.c / sim_loop.c)

Event Echo Gate

Field	Detail
Intent	Classify each decoded event and suppress its individual echo line under continue, while breakpoint matching still evaluates every event
Requirements	1.1, 1.2, 1.3, 1.4

Responsibilities & Constraints

• Structural events (always echoed, any mode): CONFIG_PUSH, JOBS_PUSH, WORKERS_PUSH, RESOURCES_PUSH, RESVALS_FULL — population/config arrivals an operator needs to see even while continue is otherwise quiet. Before printing a structural event's line, this gate calls the Round Rollup's flush entry point so any active collapsed range is closed and reported first (Requirement 3.5) — a structural event and a stale collapsed range must never interleave out of order.
• Routine events (echoed only in step mode): RESVALS_DELTA, JOB_STATE_CHANGE, JOB_UPDATE, QUEUE_UPDATE, JOB_RUSAGE. JOB_STATE_CHANGE is classified routine deliberately — the Round Rollup (Requirement 2.4) already surfaces job status transitions at round granularity, so an individual JOB_STATE_CHANGE line under continue would duplicate that information.
• Breakpoint matching (repl_find_event_breakpoint, plus the equivalent checks in xce_repl_on_begin_round/xce_repl_on_decision) runs on every event regardless of echo suppression — Requirement 1.4 is unaffected by this gate. On a match, before re-entering repl_command_loop(), the matching hook calls the Round Rollup's flush entry point so the operator sees the collapsed range's final state before the prompt returns (Requirement 3.6).

Dependencies

• Inbound: xce_repl_on_event — calls this gate before its existing breakpoint check (P0)
• Outbound: repl_print_event_summary — invoked only when the gate allows it (P0); Round Rollup's flush entry point — called before a structural-event line or a breakpoint-triggered command-loop re-entry (P0)

Contracts: Service [ ] / API [ ] / Event [ ] / Batch [ ] / State [x]

State Management

• State model: reads sim->repl_state->mode (existing field); no new state owned by this component.
• Persistence & consistency: none — a per-call decision.
• Concurrency strategy: none required — single-threaded sim driver, same as every other REPL hook.

Round Rollup

Field	Detail
Intent	Once per completed round in continue mode, compute a fingerprint and either extend an active collapsed range or flush it and begin reporting the new state
Requirements	2.1, 2.2, 2.3, 2.4, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6

Responsibilities & Constraints

• Active only while sim->interactive && rs->mode == XCE_REPL_MODE_CONTINUE; step mode keeps today's full per-decision path unchanged (Requirement 2.3, 5.1).
• Pend-jobid set is sourced by directly querying core->jobs for JOB_IS_PEND state (same iteration idiom as repl_info_jobs()) — not solely from the decision tally, so Requirement 2.4 holds independent of bug-1611 (see research.md Design Decisions).
• Dispatch/preempt counts are sourced from the existing last_n_dispatch/last_n_preempt tally.
• Must flush (print) any active collapsed range before: a breakpoint-triggered re-entry into repl_command_loop(), replay completion, or a fingerprint change from the active range (Requirement 3.5, 3.6). Because the breakpoint and structural-event triggers originate in repl_break.c, not repl.c, this component exposes a flush entry point other files call rather than owning every trigger site itself.

Dependencies

• Inbound: xce_repl_post_session_check — the round-boundary call site the fingerprint/collapse logic attaches to (P0); the Event Echo Gate (xce_repl_on_event) and the breakpoint checks in xce_repl_on_begin_round/xce_repl_on_decision (all repl_break.c) — call the flush entry point (P0); xce_repl_on_replay_complete (repl.c) — calls the flush entry point before its existing banner (P0)
• Outbound: core->jobs iterator (P0), xce_repl_on_decision's existing tally fields (P0), Jobid Range Compressor for rendering the pend-jobid list (P0)

Contracts: Service [x] / API [ ] / Event [ ] / Batch [ ] / State [x]

Service Interface

/*
 * Ends the active collapsed round range, if one is open, printing its
 * summary line immediately. Safe to call when no range is active (a
 * no-op). Called from the round boundary on a fingerprint change, and
 * from repl_break.c before a structural-event line or a breakpoint-
 * triggered command-loop re-entry, and from xce_repl_on_replay_complete
 * before its existing banner.
 */
void repl_round_collapse_flush(xce_sched_sim_driver_t* sim);

• Preconditions: sim/sim->repl_state non-NULL (same "safe no-op on NULL" discipline every other REPL hook in this file family already follows).
• Postconditions: no collapsed range is active after the call; if one was active, its summary line has been printed exactly once.
• Invariants: idempotent — calling it again immediately afterward with no intervening round is a no-op, never a duplicate print.

State Management

• State model: new fields on xce_sched_repl_state_s hold the active collapsed range (see Data Models) — whether one is open, its round/timestamp bounds, and its cached fingerprint.
• Persistence & consistency: in-memory, scoped to one REPL session; zero-initialized for free by repl_state_ensure()'s existing calloc.
• Concurrency strategy: none required — single-threaded sim driver.

Jobid Range Compressor

Field	Detail
Intent	Group a list of jobids by array base and render contiguous index runs as compressed ranges
Requirements	4.1, 4.2, 4.3, 4.4, 4.5

Responsibilities & Constraints

• Pure, read-only formatting function — never mutates its input list or any scheduler/job state.
• Shared by repl_print_event_summary()'s job-arrival listings, the Round Rollup's pend-jobid display, and repl_info_worker()'s assigned-job listing (Requirement 4.5) — the same helper, no per-caller variant.

Dependencies

• Inbound: repl_print_event_summary (P0), Round Rollup (P0), repl_info_worker (repl_info.c) (P0)
• Outbound: fmt_jobid_ex (lib/utils.c) — reuses its existing (cluster, apiserver, timestamp, job[, idx]) decomposition (P0)

Contracts: Service [x] / API [ ] / Event [ ] / Batch [ ] / State [ ]

Service Interface

/*
 * Formats `njobids` raw jobids into `buf` (bufsz-bounded): groups by
 * array base (cluster, apiserver, timestamp, job) and compresses
 * contiguous [idx] runs into [lo-hi] form, comma-joining non-contiguous
 * runs within one base; non-array jobids are listed individually.
 * Returns the number of bytes written (excluding the NUL terminator),
 * or a negative value if buf was too small to hold the full listing.
 */
int repl_fmt_jobid_range(char* buf, size_t bufsz,
                          const uint64_t* jobids, int njobids);

• Preconditions: jobids non-NULL whenever njobids > 0; buf/bufsz describe a valid, writable buffer.
• Postconditions: buf holds a NUL-terminated, comma-separated listing; distinct array bases appear in input order, indices ascend within each base's compressed ranges.
• Invariants: never fabricates or silently drops a jobid — the compressed listing always represents exactly the same id set the uncompressed listing would show.

sim_print_decision Gate

Field	Detail
Intent	Suppress sim_print_decision()'s direct per-decision stdout line when the Round Rollup will report the round instead
Requirements	2.3, 5.1

Responsibilities & Constraints

• Skip the direct print only when sim->interactive && sim->repl_state->mode == XCE_REPL_MODE_CONTINUE; step mode and non-interactive (headless) runs are unaffected (Requirement 5.1, 5.4).
• Implemented as an inline-wrapper-style gate at the existing call site in sched_sim_driver_run(), consistent with repl.h's established convention, rather than a bare if block added to the loop body.

Contracts: Service [ ] / API [ ] / Event [ ] / Batch [ ] / State [x]

State Management

• State model: reads sim->interactive and sim->repl_state->mode (both existing fields); owns no new state.

REPL Prompt Context

Field	Detail
Intent	Build the string passed to readline() each loop iteration so it shows the current session and timestamp instead of the static "(sim) " prompt
Requirements	5.5

Responsibilities & Constraints

• Applies in both step and continue modes — it changes the prompt, not any command's output, so it sits outside Requirement 5's "leave unchanged" boundary by design (Requirement 5.5 is one of that requirement's own named exceptions).
• Before any session has begun (rs->session_count == 0, the same zero-initialized value repl_state_ensure()'s calloc already guarantees), falls back to the original plain "(sim) " prompt — there is no session/timestamp to show yet, and a fabricated placeholder value would be misleading.
• Once at least one session has begun, renders "(sim session=<N> t=<human-ts>) " using rs->session_count and xce_core_now(&sim->core) formatted through the existing repl_format_ts_human() — no new timestamp source, no raw-epoch-nanosecond component (unlike the four existing t=%llu (...) print sites elsewhere in this file family, which are out of this feature's scope per Boundary Commitments). repl_format_ts_human()'s existing output is the full ISO8601 form (strftime's "%Y-%m-%dT%H:%M:%SZ", e.g. 2026-09-02T03:29:38Z), not a time-only string — the prompt reuses that format exactly rather than inventing a shorter one, since Allowed Dependencies commits to no new timestamp source.
• Uses bare rs->session_count, matching info session's/info config's existing convention (repl_info.c:848,898) — not session_count + 1. That +1 exists only in repl_print_event_summary() (repl_break.c:611) to label events echoed mid-stream, before the session containing them has finished and incremented the count; the prompt, by contrast, is only ever shown after a step/continue has returned control (i.e. after xce_repl_on_begin_round() for the just-finished session has already run), so the bare count is the session that just completed — the same number info session would report if queried at that exact prompt. Copying the +1 convention here would make the prompt disagree with info session by one.
• Built fresh on every repl_command_loop() iteration, immediately before the readline() call it feeds — never cached across iterations, since the session/timestamp can change between prompts.

Dependencies

• Inbound: repl_command_loop() (repl.c) — calls this immediately before its existing readline(XCE_REPL_PROMPT) line
• Outbound: repl_format_ts_human() (repl.c, existing), xce_core_now() (core_clock.c, existing)

Contracts: Service [x] / API [ ] / Event [ ] / Batch [ ] / State [ ]

Service Interface

/*
 * Builds this iteration's REPL prompt into `buf` (bufsz-bounded):
 * "(sim) " if no session has begun yet (rs->session_count == 0), else
 * "(sim session=<N> t=<ISO8601-ts>) " using the bare current session
 * count (NOT +1 -- see repl_print_event_summary()'s different mid-stream
 * convention) and xce_core_now()/repl_format_ts_human() (same
 * "%Y-%m-%dT%H:%M:%SZ" form used elsewhere, not a shortened one). Called
 * fresh from repl_command_loop() before every readline() -- never cached.
 */
void repl_build_prompt(xce_sched_sim_driver_t* sim, char* buf, size_t bufsz);

• Preconditions: sim/sim->repl_state non-NULL (same discipline every other REPL hook in this file family follows); buf/bufsz describe a valid, writable buffer sized for the longest possible rendering (session count width + fixed-width human timestamp).
• Postconditions: buf holds a NUL-terminated prompt string; identical across repeated calls within the same session/timestamp (a pure function of sim's current state).
• Invariants: never blocks, never reads input, never mutates sim/sim->repl_state — a read-only formatter, same class as the Jobid Range Compressor.

Resource Value Formatter

Field	Detail
Intent	Classify a resource's canonical wire unit, render its value per the operator's selected display mode, and lay out info worker's/info resource's listings as a grouped table instead of a flat line-per-resource dump
Requirements	6.1, 6.2, 6.3, 6.4, 6.5, 6.6

Responsibilities & Constraints

• Classification is a small, explicit, hardcoded name list — repl_is_bytes_valued_resource(name) returns true for exactly mem, tmp, maxmem, maxtmp, maxswap (confirmed canonical-bytes on the wire: node_information.c's node_info_get_mem()/node_info_get_tmp() docstrings, xcecd.c's init_host_attrs() bug-1554 comment). This mirrors src/controller/testsuite/test.c's is_bytes_valued_resource() exactly (same 5 names, same rationale: "a small, explicit, client-side list rather than a wire field").
• swp is a confirmed special case, deliberately not added to the bytes list: node_info_get_swap()'s own docstring states its canonical wire unit is megabytes, not bytes (unlike its maxswap counterpart, which the bug-1554 comment confirms IS bytes). Before formatting, swp's value is converted MB→bytes (× 1024.0 × 1024.0) and then passed through the same human-scaling formatter as the bytes-native resources, so it renders on the same adaptive B/KB/MB/GB/TB/PB scale rather than staying a raw MB float.
• repl_format_bytes_human(bytes, buf, bufsz) adaptively scales to the smallest unit the value fits (B/KB/MB/GB/TB/PB), mirroring test.c's format_bytes_human() algorithm exactly (divide by 1024 while >= 1024.0, cap at PB).
• Display mode (raw/human/both) is a new xce_sched_repl_state_s field, units_mode, defaulting to both (Requirement 6.3) and settable via set units raw|human|both (repl_params.c, alongside the existing speed/output/verify branches) — both renders "<raw> (<human>)", matching xce_test's own cmd_resval display convention exactly (test.c's "%f (%s)\n").
• Numeric resources with no canonical unit (load averages, factors, counts — everything not in the bytes list and not swp) print without a unit suffix, and without a trailing .00 when the value has no fractional part — replaces the current unconditional "%.2f" in repl_info.c's Value_u_fvalue branch with a conditional format.
• info worker's and info resource's resource-listing loops are rewritten from an unstructured per-resource fprintf into an aligned table, grouped into labeled sections where applicable to that listing (consumable/capacity resources with a used= split; load/utilization metrics; static hardware attributes such as type/model/cpuf/maxcpus/ndisks — info resource's cluster-wide GLOBAL/SHARED scope, per bug-1593, may not populate every section). Column widths are computed once (a shared field-width format), not hand-padded per line.
• Never alters the underlying stored/wire value or the deterministic outcome of a replay (Requirement 6.4) — display-only, same discipline test.c's own format_bytes_human() doc comment states ("the stored/wire value stays raw bytes always, this never feeds back into anything").

Dependencies

• Inbound: repl_info_worker(), repl_info_resource() (repl_info.c) (P0); repl_cmd_set() (repl_params.c) (P0)
• Outbound: none beyond standard C formatting — a self-contained classification/formatting pair, same shape as the Jobid Range Compressor

Contracts: Service [x] / API [ ] / Event [ ] / Batch [ ] / State [x]

Service Interface

/* Returns true iff `name`'s canonical wire unit is bytes (mem, tmp,
 * maxmem, maxtmp, maxswap only -- swp is handled separately, see above). */
bool repl_is_bytes_valued_resource(const char* name);

/* Adaptively scales `bytes` to the smallest unit it fits (B/KB/MB/GB/TB/
 * PB), writing e.g. "20.56 GB" into `buf` (bufsz-bounded). Display-only;
 * never touches the underlying stored value. */
void repl_format_bytes_human(double bytes, char* buf, size_t bufsz);

• Preconditions: name non-NULL for the classifier; buf/bufsz describe a valid, writable buffer for the formatter.
• Postconditions: the classifier returns a stable, name-only-dependent boolean; the formatter writes a NUL-terminated, human-readable string.
• Invariants: both are pure functions — no side effects, no dependency on REPL session state.

State Management

• State model: new units_mode field (enum raw/human/both) on xce_sched_repl_state_s, defaulting to both; read by the table-rendering code, written only by set units.
• Persistence & consistency: in-memory, scoped to one REPL session. Unless the both enumerator is deliberately assigned value 0 in its enum declaration, calloc's zero-initialization will not select it — repl_state_ensure() must explicitly set units_mode = XCE_REPL_UNITS_BOTH after allocation regardless of member order, the one field in this struct that cannot rely on zero-initialization alone (called out explicitly since every other field in this struct today deliberately relies on calloc's zero value being the correct default).
• Concurrency strategy: none required — single-threaded sim driver.

Help & Breakpoint Discoverability

Field	Detail
Intent	Reorganize help's listing into labeled, aligned sections, and expose break's complete valid-event-type set to both help and its own error message from one shared source
Requirements	7.1, 7.2, 7.3, 7.4, 7.5, 7.6

Responsibilities & Constraints

• repl_print_help() (repl.c) is rewritten into four labeled sections — Execution Control (step/continue/quit/help), Breakpoints (break/info break/delete), State Inspection (info session/job/jobs/queue/worker/resource/summary/config — info config moved here, next to its siblings, per Requirement 7.3), Snapshot & Parameters (snapshot/set speed/set output/set verify/set units) — each section using one shared field-width fprintf format (e.g. " %-38s%s\n") instead of independently hand-counted spaces per line, so a future command addition can't silently break alignment the way info config's append did.
• BP_KIND_TABLE (repl_break.c, static/file-local today) is exposed through one new shared accessor, repl_bp_kind_names(), that renders the complete comma-joined list of valid <EVENT_TYPE> tokens once. Both repl_print_help()'s break line (repl.c) and repl_cmd_break()'s unrecognized-event-type error (repl_break.c, same file as the table — a trivial local call) use this accessor rather than each hardcoding the list — the two can never drift out of sync with each other or with BP_KIND_TABLE itself (Revalidation Triggers).
• No change to which commands exist, how any command parses its arguments, or any other command's output (Requirement 7.6) — this component only touches help's rendering and the two places that now surface BP_KIND_TABLE's contents.

Dependencies

• Inbound: repl_print_help() (repl.c) (P0), repl_cmd_break()'s error path (repl_break.c) (P0)
• Outbound: BP_KIND_TABLE (repl_break.c, existing) (P0)

Contracts: Service [x] / API [ ] / Event [ ] / Batch [ ] / State [ ]

Service Interface

/*
 * Renders BP_KIND_TABLE's complete set of valid break <EVENT_TYPE> tokens
 * as one comma-joined, NUL-terminated string into `buf` (bufsz-bounded) --
 * e.g. "CONFIG_PUSH, JOB_PUSH, ..., DECISION". Used by both
 * repl_print_help() and repl_cmd_break()'s unrecognized-event-type error
 * so the two can never disagree with each other or with BP_KIND_TABLE.
 */
void repl_bp_kind_names(char* buf, size_t bufsz);

• Preconditions: buf/bufsz describe a valid, writable buffer sized for the full table (12 entries at the time of writing).
• Postconditions: buf holds every BP_KIND_TABLE token, comma-joined, in table order.
• Invariants: pure function of BP_KIND_TABLE's current contents — adding/removing a table entry changes this function's output with no other code change required.

Data Models

Domain Model

This feature adds two concepts to the REPL's existing session-scoped state (xce_sched_repl_state_s, repl_internal.h) — not a new top-level entity: a "round collapse state" (Requirements 2, 3) and an independent "resource display preference" (units_mode, Requirement 6). It follows the same pattern prior REPL task revisions used to add output_path/replay_complete to that struct.

Logical Data Model

New fields on xce_sched_repl_state_s (illustrative — exact types finalized at implementation time):

Field	Type	Purpose
collapse_active	bool	Whether a collapsed range is currently open
collapse_start_round / collapse_end_round	uint64_t	Round-number bounds of the active range
collapse_start_ts / collapse_end_ts	uint64_t	Sim-time bounds, for the collapsed range's time span (Requirement 3.4)
collapse_dispatch_count / collapse_preempt_count	int	Cached fingerprint counts
collapse_pend_jobids / collapse_n_pend_jobids	pointer + count	Cached fingerprint pend-jobid set, in whatever list form the Jobid Range Compressor consumes
units_mode	enum (raw/human/both)	Requirement 6's resource-value display mode, settable via set units; defaults to both

Consistency & Integrity: all fields reset together whenever a range flushes (print, then clear) or a new REPL session begins — repl_state_ensure()'s existing calloc zero-initializes new fields with no additional lifecycle code required, except units_mode: unless both is deliberately given enum value 0, calloc's zero-initialization will not select it, so repl_state_ensure() must explicitly set it to both after allocation regardless of the enum's member order — the one field in this struct where zero-initialization alone cannot be relied upon to be the correct default.

No Physical Data Model, API Data Transfer, or Event Schema subsections apply: this feature has no persistent storage, no network wire format, and adds no new wire-level contract — it stays inside scheduler-core's existing "simulation isolation" boundary (repl.h's own header comment: no scheduler.h, no client.h, no capnp types).

Error Handling

Error Strategy

Consistent with existing repl.c/repl_break.c conventions: allocation failures print an existing-style "[sim] ..." message and degrade to the safest available behavior rather than crashing or losing information, matching repl_state_ensure()'s own "never load-bearing, degrade to unattended" precedent.

Error Categories and Responses

• Allocation failure while building a round's fingerprint or growing the collapsed-range pend-jobid buffer: fall back to printing that round's line directly (uncollapsed) rather than losing the round's information — preserves Requirement 2.1's obligation to report every round with decisions.
• repl_fmt_jobid_range() buffer too small: returns a negative value; the caller falls back to the existing uncompressed per-id listing for that call — never truncates silently, never crashes, preserves the "never drop a jobid" invariant even in a buffer-constrained edge case.

Monitoring

No new logging framework is introduced — the existing [sim] ... stdout convention remains the only user-facing signal; this is an interactive CLI tool, not a daemon, so no zap/WARN-level logging applies here.

Testing Strategy

Unit Tests (new test_repl_output_compression.c)

• Contiguous indices from one array base compress to a single [lo-hi] range (Requirement 4.1).
• Non-contiguous indices compress to comma-joined sub-ranges within one base (Requirement 4.2).
• Multiple array bases in one listing compress independently (Requirement 4.3).
• A mixed array + non-array listing shows non-array ids individually and compresses only the array ids (Requirement 4.4).
• A buffer too small to hold the full listing returns a negative value and writes nothing past bufsz (Error Handling).

Unit Tests (new test_repl_resource_formatting.c)

• repl_is_bytes_valued_resource() returns true for exactly mem, tmp, maxmem, maxtmp, maxswap, and false for swp, unitless resources (e.g. r1m), and an unknown/custom name (Requirement 6.1).
• repl_format_bytes_human() adaptively scales across the full B/KB/MB/GB/TB unit range, including exact boundary values (e.g. exactly 1024 bytes renders as 1.00 KB, not 1024.00 B) (Requirement 6.2).
• swp's value is converted MB→bytes before formatting, so a raw swp value renders on the same adaptive scale as a byte-native resource of equivalent magnitude (Requirement 6.1).
• A whole-number unitless value (e.g. 22.0) renders with no trailing .00; a fractional one (e.g. 0.57) still renders with its decimal places (Requirement 6.5).

Integration Tests (extend test_repl_breakpoints_inspection.c, test_repl_snapshot_params.c)

• set units raw/set units human/set units both each select the corresponding rendering for a subsequent info worker/info resource call; an unrecognized set units value is rejected with the existing set: unrecognized parameter error shape (Requirement 6.2, 6.3).
• info worker's resource listing renders as a grouped, aligned table with used= shown only for consumable/capacity resources, matching the hand-validated shape against a real captured worker's resource dump (Requirement 6.6).
• info worker's assigned-job listing, given a job array's worth of contiguous indices, renders as a single compressed range via the same helper Requirement 4 already covers (Requirement 4.5).
• break's unrecognized-event-type error message lists the complete, current BP_KIND_TABLE token set (Requirement 7.5).

Integration Tests (extend test_repl_execution_control.c, child-process output capture)

• continue across multiple idle rounds (zero decisions) produces one collapsed range line, not one line per round (Requirement 3.1).
• continue across rounds sharing an identical nonzero pend set produces one collapsed "unchanged" range line — the exact shape hand-validated against the real 108-round replay that motivated this spec (Requirement 3.2).
• A structural event mid-continue ends any active collapsed range and prints its own line before continuing (Requirement 1.3, 3.5).
• A breakpoint hit mid-collapse flushes the active range before entering the command loop (Requirement 3.6).
• Replay completion (EOF) flushes any active collapsed range before the existing "replay complete" banner (Requirement 3.6).
• step-mode output is unchanged versus this feature's pre-implementation baseline — regression check alongside the existing test_should_pause_fires_on_exactly_the_nth_session-style fixtures (Requirement 5.1, 5.3).
• A job's tracked status changing between rounds is reflected in the next round summary even under a fixture that never emits a synthetic DISPATCH decision — exercises the state-derived-pend-set design decision independent of bug-1611's resolution (Requirement 2.4).
• The REPL prompt is the plain "(sim) " before any session begins, then includes the current session count and a human-readable timestamp once at least one session has run, in both step and continue modes (Requirement 5.5).
• help's output groups commands into the four labeled sections, uses one consistent column width throughout, lists info config alongside the other info subcommands, and includes the complete break event-type list (Requirement 7.1-7.4).

E2E

Not applicable beyond the integration tests above — this feature has no HTTP/API surface; the child-process harness already exercises the real xce_scheduler binary end-to-end at the process level.

Optional Sections

Security Considerations, Performance & Scalability, and Migration Strategy are omitted: this is a local, single-operator interactive CLI output change with no new attack surface, no persistent or high-load data path (round counts are bounded by replay length, already tolerated by existing step output), and no schema or data migration.

Supporting References

None beyond research.md — no external API, vendor library, or long schema requires separate documentation.