feat(sessions): add zero sessions prune, which never removes a session another process has open

[Vasanthdev2004]

Closes #971

What

zero sessions prune removes saved sessions that haven't been updated for a while, in the shape approved on #971:

• It only runs when you run it. Nothing in Zero calls it on its own.
• --older-than 30d (days, or a Go duration such as 720h) sets the cutoff, and it is never under a day. --dry-run lists what would go and why the rest stays. It makes every check a real run makes, including the ones made once a session is held for removal, and removes nothing. --json prints the report.
• Without --older-than it uses sessions.retentionDays from your user config. With neither it refuses and says how to set one, so nothing is removed unless a cutoff was asked for.

Output from a build of this branch on Windows, against six sessions: two old and idle, one old but held open by another process, one old parent of a recent fork, and two recent ones, which aren't listed:

$ zero sessions prune --older-than 30d --dry-run
Would remove 2 sessions last updated before 2026-08-27T06:07:37Z (2.5 KB):
  zero_20260701101112_1782900672000000000_1  2026-07-01  refactor the parser
  zero_20260715164503_1784133903000000000_1  2026-07-15  flaky test in the tui
Kept 2 old enough to remove:
  zero_20260702080000_1782979200000000000_1  2026-07-02  open in another Zero process
  zero_20260612093015_1781256615000000000_1  2026-06-12  parent of a session that is kept
Dry run: nothing was removed.

$ zero sessions prune --older-than 12h
[zero] sessions prune does not remove anything updated in the last 24 hours; use --older-than 1d or more

$ zero sessions prune
[zero] sessions prune needs a cutoff: pass --older-than (for example --older-than 30d) or set sessions.retentionDays in your user config

The real run printed the same two lists under Removed 2 sessions, and afterwards exactly those two session directories were gone and the other four were untouched. Once the process holding the open one exited, a dry run listed it for removal, so a lease doesn't outlive its process.

What it never removes

• A session another Zero process has open. A session held no lock between writes, so nothing could tell a prune in one terminal that another terminal still had it open. Each session now has a lease.lock. A process that creates a session, writes to it, or loads it through the rehydrated read that the TUI's resume, exec --resume and ACP's session/load all use holds a shared lock on it for its lifetime. Prune takes the lock exclusively and skips any session it can't get. Taking a lease never waits. A write that finds prune holding the session carries on, because it lands under the write lock, where prune checks the session again: prune either sees the write and keeps the session, or the write finds it gone. A read changes nothing prune checks, so loading a session to continue it (the TUI's resume, exec --resume and --fork, ACP's session/load and session/resume) is refused at that moment with "locked by zero sessions prune; try again", and none of them falls back to a raw read on it. Those callers picked the session from its metadata a moment before they read it, so HoldToContinue also requires that metadata once the lease is held: a session prune removed in between, part way or completely, is refused instead of continued as an empty conversation. The one-day floor covers older Zero builds, which take no lease: anything they are actively using has been written within a day.
• A session being forked, or given a child. Every way of creating a session under a parent holds that parent first and keeps it: Fork, CreateChild, and Create with a parent, which exec --calling-session-id and spec implementations use. Each is refused while prune holds the parent, and also when the parent's directory is still there without its metadata. Prune removes the metadata first and unlinks lease.lock after it, so a lease taken at that moment lands on a fresh lease file and proves nothing.
• An ancestor of a session that stays. Lineage and Tree fail on a missing ancestor. Descendants are removed before their ancestors, so one that turns out to be open part way through still keeps every ancestor above it. A child created after the plan, by a process that has exited since, isn't in the plan, so once prune holds a parent exclusively it looks for sessions the plan didn't see that name it, and keeps the parent if there is one. Nothing can create a new child while that lease is held.
• A session written between the plan and its removal, which is checked again under its lease and write lock, or one whose last update time can't be read.
• A session whose lease can't be taken at all, for instance on a filesystem without lock support. A process that can't take the lease there still resumes and forks the session, since prune can't remove it either.

How a session is removed

The metadata goes first, while both locks are held. From that point List and Get no longer show the session, so a removal that fails part way leaves nothing that looks like a session, and the command exits non-zero with the session under Could not remove. The rest follows, checkpoint blobs included since they live inside the session directory, and session.lock and the directory itself go last, once the write lock is released. On Windows lease.lock is opened with FILE_SHARE_DELETE, so a held lease never blocks removing the directory, including a test's temp-directory cleanup. Without it, prune can't delete the lease file it is itself holding, which is the P12 row below. Prune lets go of that lease just before the directory goes: where a delete only takes effect once the last handle closes (Windows without POSIX delete semantics, as on older builds or FAT and exFAT volumes), its own handle would keep the directory from being empty.

The retention setting is yours, not the repository's

sessions.retentionDays is read straight from the user config file, and no resolver merge copies it from anywhere. A project's .zero/config.json can't decide what prune deletes: TestSessionsPruneIgnoresRetentionInProjectConfig sets it to one day in the workspace and prune still asks for a cutoff.

Verification

New tests: 12 in internal/sessions/prune_test.go and 3 in prune_race_test.go, 10 in internal/cli/sessions_prune_test.go, 4 in internal/config/sessions_config_test.go, and two each in internal/tui and internal/acp.

Each of these edits to the branch fails a test, for the reason shown. All 44 ran on Windows and none of them is a compile failure.

	Edit	Fails with
P1	no lease check while planning	dry run kept reason "" and would remove [old], want it kept as open
P2	writes take no lease	the same, for the session another process wrote
P3	rehydrated reads take no lease	the same, for the session another process resumed
P4	Create takes no lease	kept reason "", want "open in another Zero process"
P5	no ancestor rule while planning	removed "parent,grandparent,unrelated", want only the unrelated session
P6	no ancestor rule while removing	parent kept for "", want "parent of a session that is kept"
P7	ancestors removed before descendants	removal reached [parent child], want the child first and the parent never
P8	no re-check under the locks	child kept for "", want "updated while pruning"
P9	no one-day floor in the store	a 23h cutoff was not refused for being under the minimum
P10	a dry run removes	a dry run removed old-a
P11	undated sessions planned for removal	dry run kept reason "" and would remove [undated]
P12	lease.lock opened without FILE_SHARE_DELETE	removed "", want old-a,old-b
C1	CLI floor check removed	--older-than 12h: exit 1 ... want a usage error naming "last 24 hours"
C2	retention setting ignored	exit 2, stderr "[zero] sessions prune needs a cutoff ..."
C3	prune flags accepted by other commands	[list --dry-run]: exit 0, stderr ""
K1	setting dropped when the config is written	after an unrelated write retentionDays = 0, want 21
K2	negative retention accepted	a negative retention was accepted
F1	Fork does not hold its parent	fork from a parent prune holds: err = <nil>, want it refused
F2	CreateChild does not hold its parent	child from a parent prune holds: err = <nil>, want it refused
F3	a busy lease is never reported	both of the above
F4	Fork lets the parent go when it returns	parent kept for "parent of a session that is kept", want "open in another Zero process"
L1	the lease is let go only when pruneSession returns	old: the directory is removed while prune still holds the lease
E1	an empty flag value is accepted	["prune" "--older-than" ""]: exit 0, stderr "", want a usage error, and the retention setting removes a session
R1	the rehydrated read takes the lease best effort again	rehydrated read while prune holds the session: err = <nil>, want ErrPruning, and the TUI and ACP tests below
R2	exec falls back to the raw log on ErrPruning	exec context read while prune holds the session: 1 events, err = <nil>, want it refused, not read from the raw log
R3	the TUI resume falls back to the raw log	resume while prune holds the session: 1 events, err = <nil>, want it refused
R4	ACP loadHistory falls back to the raw log	session/load while prune holds the session: err = <nil>, want it refused, and the same for session/resume
R5	ACP load publishes a session prune holds	a session refused while prune held it was still promptable
N1	planning treats a lease it cannot take as free	dry run true: kept for "", removed [old], failed [], want it kept because its lease could not be checked
N2	a reader fails closed when it cannot take the lease	resume a session whose lease cannot be taken: zero session old is locked by zero sessions prune; try again
A1	no look for children made after the plan	parent kept for "", want "parent of a session that is kept" (removed [parent]), and the late fork's Lineage fails
A2	Create with a parent does not hold it	the create, exec calling-session and spec implementation legs are not refused
A3	HoldToContinue does not require the metadata	the continuation, exec, TUI and ACP reads of a removed session all succeed
A4	the hold on a parent accepts one being removed	create a session under one prune is removing: err = <nil>, want it refused
A5	the stray lease file is left behind	removed [], failed [old]: the refused continuation must not keep prune from removing the directory
A6	the TUI resume does not hold what it picked	resume while prune is removing the session: 1 events, err = <nil>, want it refused
A7	exec does not hold what it picked	exec context read of a session prune is removing: 0 events, err = <nil>, want it refused
A8	ACP does not hold what it picked	load history of a session prune is removing: err = <nil>, want it refused
D1	a dry run lists every planned session without the checks made at removal	dry run true: the report is removed [parent] kept [] failed [], want removed [] kept [parent: parent of a session that is kept] failed [], and the same for a write and an open since the plan
D2	a dry run skips the look for children made after the plan	the fork case above
D3	a dry run skips the re-read of the last update	the fork case, and removed [child parent] kept [] for the write
D4	a dry run skips the second lease check	all three, including removed [opened idle] kept [] for the open
D5	a dry run removes the metadata before it stops	the dry run removed the metadata of idle
D6	a dry run reports what it could not check under Could not remove	dry run report: without Could not check 1:

On Windows 11:

• go test ./...: everything passes except the two tests test(config,tui): stop two tests reading the developer's environment and checkout path #1072 fixes, which fail the same way on main on this machine. In the last full run TestACPEndToEndPrompt also timed out once (session/prompt: context deadline exceeded) while I was building a second checkout alongside it. It passed five runs on its own and two runs of the whole internal/acp package, and the dry-run change doesn't touch ACP.
• go test -race ./internal/sessions/ ./internal/acp/: 19 of 20 runs pass, ten of them while the full suite ran alongside. The one failure was in internal/sessions, on the first run after the previous round of changes. A tail cut its output and it never came back, so I can't name the test. After the dry-run change, five more runs of go test -race ./internal/sessions/ pass.
• gofmt, go vet ./..., and go vet of the changed packages with GOOS=linux and GOOS=darwin: clean.
• golangci-lint (unused,ineffassign,staticcheck) on the changed packages: clean for windows and darwin. For linux it reports SA5011 in internal/cli/exec_test.go and three internal/tui test files, none of which this branch touches, and main reports the same.
• go run ./cmd/zero-release build and smoke, govulncheck ./..., git diff --check: clean.

lease_unix.go takes the lease with flock, which I can't run on this machine. flock locks belong to the open file description, so two opens in one test process conflict the way two processes do. The prune tests pass in CI's Linux, macOS and race jobs, and TestPruneLeavesASessionAnotherProcessHasOpen can only pass there through the branch where the lock is refused, since that is the only place the "open in another Zero process" reason comes from.

A lease lives as long as its process, one file descriptor per session that process has touched. A long TUI or ACP run holds one for every session it created, resumed or wrote, child sessions included, and a session the TUI switched away from with /new stays held until it exits. That errs toward keeping, and a session used that recently is not a candidate anyway. Store.Release is there for letting go on a switch, but nothing calls it yet.

Summary by CodeRabbit

• New Features
  • Added zero sessions prune to remove sessions older than a specified cutoff, with a dry-run option and text or JSON reports.
  • When no cutoff is provided, pruning uses the retention period configured in user settings. Cutoffs must be at least 24 hours old.
• Bug Fixes
  • Prevented sessions from being resumed or modified while they are being pruned. Active sessions and their ancestors are kept.

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Walkthrough

Adds zero sessions prune with configurable cutoff selection, dry-run and JSON output, lease-aware session pruning, and protection for active sessions and retained lineage.

Changes

Session pruning

Layer / File(s)	Summary
Retention configuration internal/config/types.go, internal/config/sessions_config.go, internal/config/*_test.go	Adds sessions.retentionDays, validates its value, loads user session settings, and tests serialization and loading.
Session lease tracking internal/sessions/lease*.go, internal/sessions/store.go, internal/sessions/lineage.go, internal/sessions/replay.go, internal/sessions/exec_session.go, internal/acp/agent.go, internal/acp/agent_test.go, internal/tui/session.go, internal/tui/resume_pruning_test.go	Adds shared and exclusive leases. Session operations acquire holds, and reads or activation paths return sessions.ErrPruning when pruning is in progress.
Prune selection and removal internal/sessions/prune.go, internal/sessions/prune_test.go, internal/sessions/prune_race_test.go	Adds Store.Prune, protection for open, undated, updated, and ancestor sessions, removal reporting, dry-run checks, and race coverage.
CLI command and reporting internal/cli/sessions.go, internal/cli/sessions_prune.go, internal/cli/sessions_prune_test.go, README.md, README_ZH.md	Adds the prune command, cutoff parsing, user-config fallback, text and JSON reports, flag validation, tests, and documentation.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Feature · Severity of issue fixed: Medium

Suggested reviewers: euxaristia, jatmn

Sequence Diagram(s)

sequenceDiagram
  participant User
  participant runSessionsPrune
  participant config.ReadSessionsConfig
  participant Store.Prune
  User->>runSessionsPrune: Invoke prune with cutoff options
  opt No explicit cutoff
    runSessionsPrune->>config.ReadSessionsConfig: Read user retention settings
    config.ReadSessionsConfig-->>runSessionsPrune: Return retention days
  end
  runSessionsPrune->>Store.Prune: Submit cutoff age and dry-run option
  Store.Prune-->>runSessionsPrune: Return prune report
  runSessionsPrune-->>User: Write text or JSON report

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Merge Risk: 🟡 Moderate · up to ff04d

An explicitly empty cutoff can cause pruning under the configured retention period instead of returning a usage error. Fix the flag validation before merging.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 49.28% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 69 functions across 20 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The PR meets the relevant coding objectives in [#971]. It adds the manually invoked zero sessions prune command with cutoff validation, sessions.retentionDays fallback, dry-run mode, JSON output, …
Out of Scope Changes check	✅ Passed	The changes stay within [#971]. CLI and README updates expose session cleanup. Configuration provides the retention default. Lease, lineage, access-path, and race-handling changes protect session data…
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding the zero sessions prune command with protection for sessions open in another process.

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Inline comments:
In `@internal/cli/sessions.go`:
- Around line 180-187: Validate the separate-argument value in the
`--older-than` case using `parseNonEmptySessionsFlag` before assigning it to
`options.olderThan`; return its error through the existing error path so empty
values are rejected for both `sessions prune` and `sessions list`.

In `@internal/sessions/prune.go`:
- Around line 280-305: Update pruneSession to close and unlock the lease after
removing the session lock but before removing the session directory; make the
deferred cleanup safe if the lease has already been closed. Preserve lease
cleanup on earlier return paths.

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• README.md
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• internal/cli/sessions.go
• internal/cli/sessions_prune.go
• internal/cli/sessions_prune_test.go
• internal/config/sessions_config.go
• internal/config/sessions_config_test.go
• internal/config/types.go
• internal/sessions/lease.go
• internal/sessions/lease_unix.go
• internal/sessions/lease_windows.go
• internal/sessions/lineage.go
• internal/sessions/prune.go
• internal/sessions/prune_test.go
• internal/sessions/replay.go
• internal/sessions/store.go

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Head: ff04d2fcd185
Changed files (22): README.md, README_ZH.md, internal/acp/agent.go, internal/acp/agent_test.go, internal/cli/sessions.go, internal/cli/sessions_prune.go, internal/cli/sessions_prune_test.go, internal/config/sessions_config.go, internal/config/sessions_config_test.go, internal/config/types.go, internal/sessions/exec_session.go, internal/sessions/lease.go, and 10 more

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⚠️ Outside diff range comments (1)

🟡 Minor · Propagate a busy lease result before accessing the session. · lease.go:29-35

internal/sessions/lease.go:29-35
🩺 Stability & Availability | 🟡 Minor | ⚡ Quick win

Suggested fix

-func (store *Store) Hold(sessionID string) {
-	store.hold(sessionID)
+func (store *Store) Hold(sessionID string) bool {
+	return store.hold(sessionID)
 }

Propagate a busy lease result before accessing the session.

hold returns busy=true when Prune owns the exclusive lease, but Hold discards that result. Rehydrated reads and lockSession continue without a shared lease. Exec, ACP, and TUI then fall back to raw reads, which also do not acquire a lease. Prune can remove the metadata, event log, and session directory during these operations. Reads can return empty history, and writes can fail against the removed session.

After exposing the result, update every caller to stop or propagate a distinct busy error. The fallback readers must not convert that error into a raw-read fallback. lockSession must return before taking the session locks. holdParent already follows this pattern by rejecting a busy parent.

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In `@internal/sessions/lease.go` around lines 29 - 35, Store.Hold discards the
busy result from store.hold, allowing session operations to continue without a
lease while Prune owns it. Return the lease result from Hold and update its
callers to stop or propagate a distinct busy error; ensure rehydrated reads and
raw-read fallbacks preserve that error, and make lockSession return before
taking session locks, following holdParent’s existing pattern.

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Outside diff comments:
In `@internal/sessions/lease.go`:
- Around line 29-35: Store.Hold discards the busy result from store.hold,
allowing session operations to continue without a lease while Prune owns it.
Return the lease result from Hold and update its callers to stop or propagate a
distinct busy error; ensure rehydrated reads and raw-read fallbacks preserve
that error, and make lockSession return before taking session locks, following
holdParent’s existing pattern.

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Inline comments:
In `@internal/sessions/lease.go`:
- Around line 39-55: Update hold to return lease acquisition errors from
openLeaseFile and tryLockLease separately from normal lock contention, and
propagate those errors through holdOrRefuse while preserving ErrPruning for
contention. Update callers of hold, including Hold, to handle its new result.

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• internal/acp/agent.go
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• internal/sessions/exec_session.go
• internal/sessions/lease.go
• internal/sessions/lineage.go
• internal/sessions/prune.go
• internal/sessions/prune_test.go
• internal/sessions/replay.go
• internal/sessions/store.go
• internal/tui/resume_pruning_test.go
• internal/tui/session.go

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[Vasanthdev2004]

@coderabbitai on the outside-diff note about Hold dropping the busy result: right for reads, and fixed in 7fa20170. Writes are left alone on purpose.

A read that continues a session changes nothing prune checks again, so a resume that started while prune held the session went on using one prune was free to remove. The rehydrated read now fails with ErrPruning at that moment, and the TUI resume, exec --resume and --fork, and ACP's loadHistory don't fall back to a raw read on it. ACP's session/load stays best effort about a history it can't read, but refuses this one instead of publishing the session. TestResumeIsRefusedWhilePruneHoldsTheSession, TestResumeEventsIsRefusedWhilePruneHoldsTheSession and TestACPLoadAndResumeAreRefusedWhilePruneHoldsTheSession cover the three paths, and each one fails when its own guard is taken out.

A write doesn't need the refusal. It lands under session.lock, where prune reads the metadata again before removing anything. Either the write lands first and prune keeps the session as updated while pruning, which TestPruneKeepsTheAncestorsOfASessionWrittenWhilePruning drives through a seam, or prune has already removed the metadata and appendPreparedEventsLocked fails reading it, before it writes an event. So lockSession still takes the lease best effort.

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🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
set -euo pipefail
for f in internal/sessions/lease.go internal/sessions/prune.go internal/sessions/store.go internal/sessions/replay.go internal/sessions/exec_session.go internal/sessions/lineage.go internal/tui/session.go internal/acp/agent.go internal/sessions/prune_test.go internal/tui/resume_pruning_test.go internal/acp/agent_test.go; do
  echo "=== $f ==="
  ast-grep outline "$f" --items all --match 'Hold|holdOrRefuse|HoldExclusive|Prune|prune|lockSession|appendPreparedEventsLocked|ReadRehydratedEventsWithPresence|readExecContextEvents|resumeEvents|loadHistory|TestResume|TestPrune|TestACP|CreateChild|Fork' | head -85 || true
done
git show --stat --oneline 7fa20170 --  internal/sessions internal/tui internal/acp | head -80

Length of output: 8477

---

🏁 Script executed:

#!/bin/bash
set -euo pipefail
rg -n -C4 'func .*holdOrRefuse|func .*HoldExclusive|func .*Hold\(|func .*Prune\(|func .*lockSession\(|func .*appendPreparedEventsLocked|func .*ReadRehydratedEventsWithPresence|func .*readExecContextEvents|func .*resumeEvents|func .*loadHistory|TestPruneKeepsTheAncestorsOfASessionWrittenWhilePruning' internal/sessions internal/tui internal/acp | head -250

Length of output: 8511

---

🏁 Script executed:

#!/bin/bash
set -euo pipefail
git status --short

Length of output: 189

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🏁 Script executed:

#!/bin/bash
set -euo pipefail
for spec in \
'internal/sessions/lease.go:25:135' \
'internal/sessions/prune.go:90:193' \
'internal/sessions/prune.go:237:320' \
'internal/sessions/store.go:655:700' \
'internal/sessions/store.go:907:955' \
'internal/sessions/store.go:433:455' \
'internal/sessions/replay.go:230:260' \
'internal/sessions/exec_session.go:154:172' \
'internal/tui/session.go:312:329' \
'internal/acp/agent.go:899:936' \
'internal/sessions/prune_test.go:260:294' \
'internal/sessions/prune_test.go:418:490' \
'internal/tui/resume_pruning_test.go:1:48' \
'internal/acp/agent_test.go:2425:2468'; do
 f="${spec%%:*}"; r="${spec#*:}"; a="${r%%:*}"; b="${r##*:}"
 echo "=== $f:$a-$b ==="; sed -n "${a},${b}p" "$f"
done
rg -n -C3 'ErrPruning|loadHistory\(' internal/acp/agent.go internal/sessions/exec_session.go internal/tui/session.go

Length of output: 31038

---

@Vasanthdev2004, I verified the fix in 7fa20170. Rehydrated reads now return ErrPruning when prune holds the lease. The TUI, exec, and ACP paths do not fall back to raw reads on that error. The named tests cover those refusal paths.

I also checked the write path. Prune rereads metadata under session.lock before removal. appendPreparedEventsLocked reads metadata before writing an event, so a write that acquires the lock after metadata removal fails. The write-path distinction is sound. I did not run the tests.

Thanks for the explanation.

---

✏️ Learnings added

Learnt from: Vasanthdev2004
URL: https://github.com/Gitlawb/zero/pull/1089

Timestamp: 2026-09-26T16:28:53.593Z
Learning: In `internal/sessions` for the Go `zero sessions prune` command, reads that continue a session and operations that create a child or fork use `holdOrRefuse` to return `ErrPruning` if prune holds the exclusive lease. Writes through `Store.lockSession` keep `Store.Hold` best effort because prune rereads metadata under `session.lock` before removal, and `Store.appendPreparedEventsLocked` fails before writing an event if metadata has already been removed.

Note: Learnings are effective only in the context of similar code segments. To apply general coding guidelines, please configure review instructions. You can manage existing learnings in the app.

You are interacting with an AI system.

[jatmn]

I found issues that need to be addressed before this is ready.

Merge readiness

The PR head is dc3ec65100c42f2b9d77e024f459e5c990dbf27b; the live main head and merge base are both 99721c762f37cd43ac511007a5f51d1846df959e. GitHub reports mergeable: true, no conflicts, and all reported CI checks passing. Its merge state is blocked pending the normal review requirements; I found no rebase or duplicate-PR blocker. The earlier #982 attempt closed without merging; #1091 concerns daemon in-memory session capacity.

Findings

🟠 P1 — Preserve newly created descendants when pruning an old parent

📍 Where: internal/sessions/prune.go:98-188,237-282, internal/sessions/exec_session.go:131-147, and internal/sessions/store.go:287-339.

💥 What fails: Prune snapshots descendants once. A separate process can fork an old parent after that scan and exit before prune reaches it. The fork remains recent, but the parent's timestamp is unchanged, so prune removes the parent. A second path, zero exec --calling-session-id, can create a child while prune already holds the parent's exclusive lease, because it calls Get(parent) and then direct Create(child) without checking the parent lease. Either path leaves a child whose Lineage and Tree fail on the missing ancestor. Isolated Go overlay probes reproduced both interleavings without editing the checkout.

🔎 Root cause: The parent/descendant safety rule is enforced for Fork and CreateChild and for descendants present in prune's initial scan, but the direct parent-bearing Create path bypasses admission, and the final parent deletion check never looks for a descendant created after that scan. EnsureSpecImplementation is another direct parent-bearing Create consumer; its best-effort write lock does not refuse a busy parent lease.

📜 Stated contract:

“Either a session that is still the parent of a kept session is not a candidate, or Lineage and Tree stop at a missing ancestor instead of failing.” — maintainer's approved #971 guidance

🏷️ Attribution: PR-introduced and PR-activated. The merge-base and live target have the child creation paths, but no prune operation that can remove their parent. This head adds the one-time ancestry plan and exclusive lease while leaving these creation/final-check edges incomplete.

📌 In this PR:

• prune.go — initial descendant snapshot and final parent removal; the final check reads only the parent's age.
• exec_session.go and changed Store.Create — direct parent-bearing child creation, including --calling-session-id, does not refuse the parent's exclusive lease. EnsureSpecImplementation reaches the same changed Create path.
• Fork and CreateChild — correctly refuse a busy parent lease, but a completed fork created after the snapshot is absent from the plan.
• internal/sessions/prune_test.go — tests initial ancestors and the Fork/CreateChild busy-lease paths; no test covers either reproduced interleaving.
• internal/cli/sessions.go help — promises prune keeps an ancestor of a session it keeps; that promise must describe the corrected behavior.

🔒 Unchanged on main: EnsureSpecImplementation itself and the existing lineage behavior need no general rewrite. Its route is newly exposed to pruning through the PR's changed Store.Create and prune path.

🔧 Required correction: Apply the existing parent-lease refusal rule to parent-bearing creation through the changed Create/exec path, including the spec consumer, and make the final parent removal decision account for descendants added after planning while the parent is exclusively held. Keep each ancestor above a retained descendant. Add regression controls that fail for both the direct-create-while-busy and completed-fork-after-scan cases. Keep the in-diff CLI help claim accurate.

🛠️ Author fix: Close both missing edges on every in-diff row in one pass. A fix limited to --calling-session-id leaves the completed-fork race; a final rescan alone leaves child creation possible during the exclusive hold. Use the existing lease/lineage rules at these PR paths; do not rebuild unrelated session machinery.

🚫 Out of scope: Changing Lineage/Tree to tolerate missing ancestors, rewriting all parentless Create calls, or redesigning the existing session lock framework.

---

🟡 P2 — Refuse continuation after prune has removed the session metadata

📍 Where: internal/sessions/prune.go:280-318, internal/sessions/replay.go:242-255, and the changed exec, TUI, and ACP continuation paths.

💥 What fails: Removal deletes metadata.json and lease.lock before it removes the directory. A continuation can read metadata just before prune starts, then reach the lease check after the old lease file is unlinked. It opens a new lease.lock inode, gets a shared lock, and reads a missing event log as empty history without ErrPruning. The exec and TUI resume paths can then continue a session whose metadata and event log are gone; ACP session/load can publish it as promptable. An isolated overlay probe reproduced a successful empty rehydrated read during prune cleanup after a prior Get.

🔎 Root cause: The new lease check treats acquiring any file at lease.lock as proof that the previously read session still exists. Unlinking and recreating that pathname during deletion breaks the identity of the lock. The changed high-level continuation paths only reject ErrPruning; they do not verify the previously selected metadata remains live after a successful read.

📜 Stated contract:

“a hard rule that the session currently being resumed or forked is never a candidate.” — maintainer's approval on #971

The PR's changed ACP activation comment also says load must not publish a session that prune may be removing.

🏷️ Attribution: PR-introduced and PR-activated. The merge-base and live target have the low-level empty-on-missing read behavior, but no zero sessions prune cleanup that unlinks the lease under a concurrent continuation. This head adds that deletion sequence and the new lease-based continuation gate.

📌 In this PR:

• prune.go — removes the lease pathname and releases its handle before directory removal.
• replay.go — rehydrated read can lock a recreated lease inode and return empty-success after metadata disappeared; its existing empty-on-missing API behavior must be preserved.
• exec_session.go and tui/session.go — resume callers accept the successful empty read after selecting the prior metadata.
• acp/agent.go — session/load can publish that successful empty read; session/resume refuses a missing event log when its prior event count is positive, but zero-event sessions remain exposed.
• Changed sessions, TUI, and ACP tests — assert refusal while the original exclusive lease is held, but not after lease unlink during cleanup.
• internal/cli/sessions.go help — its open-session safety promise depends on this continuation boundary.

🔒 Unchanged on main: The low-level ReadRehydratedEvents empty-on-missing contract and unrelated manual filesystem deletion behavior are outside this fix.

🔧 Required correction: At the PR's continuation/activation boundary, ensure a read based on previously selected metadata cannot return or publish a resumable session after prune has removed that metadata, even if a new lease inode was acquired. Cover the unlink-to-directory-removal interleaving and the distinct exec, TUI, and ACP effects with focused regression evidence. Preserve the low-level empty-on-missing behavior for callers without a previously selected session.

🛠️ Author fix: Close the live-session identity gap across every listed in-diff continuation path in one pass; do not patch only one ErrPruning branch. Keep the correction local to the PR's prune and continuation code, and do not turn unrelated read failures into prune contention.

🚫 Out of scope: Replacing OS locking, changing unrelated raw reads, or changing ACP's separate sub-run permission policy.

[euxaristia]

Explicit user-run command only, refuses without a cutoff, minimum age 24h, the lease is shared-by-holders and exclusive-by-prune and never waits, ancestors of kept sessions are kept with a cycle-safe walk, and the re-check under the session lock means a racing writer at worst leaves an empty directory. Nothing automatic, matching the approved design.

[Vasanthdev2004]

@jatmn all three were real, thanks. Fixed in 94c90879.

P1, the fork made after the plan. Once prune holds a parent exclusively, it now looks for sessions the plan didn't see that name that parent. That costs one directory listing plus whatever was created since the plan, and prune keeps the parent if it finds one. The check is only sound because nothing can create a child while the parent is held exclusively, which is the second half.

P1, direct creation under a parent. Store.Create with a ParentSessionID now holds the parent the way Fork and CreateChild do. So exec --calling-session-id and EnsureSpecImplementation are refused while prune holds it. TestForkAndChildHoldTheParentTheyAreCreatedFrom has legs for both now, plus a plain Create. TestPruneKeepsAParentForkedAfterThePlan forks the parent from a separate store, in a seam between the plan and the removals, and then lets that store exit. Without the new check, prune removes the parent and the fork's Lineage fails with zero session not found: parent.

P2, continuing a session prune removed. As you said, a lease on a fresh lease.lock proves nothing. There are now two checks, both made after the lease is held:

• HoldToContinue requires the metadata of a session the caller picked. The TUI resume, exec --resume and --fork, and ACP's loadHistory go through it. They're refused with an error matching ErrPruning both part way through the removal and after it, zero-event sessions included. ACP's activation then refuses the load the same way it does for a held session.
• The hold on a parent refuses one whose directory is still there without its metadata.

A refused caller gives the lease back and removes the stray lease file, so prune still removes the directory. TestContinuingASessionPruneIsRemovingIsRefused runs the real interleaving through a seam just before the directory removal, with the metadata and the old lease file already gone. It checks that the continuation, the exec read and a create under that session are all refused, and that prune still reports the session removed. The rehydrated read on its own still reads a session that never existed as empty.

Each piece fails its test when taken out: eight edits in all, one per piece, each caught at its own layer (sessions, TUI, ACP). The help text's promise holds as written.

[jatmn]

I found issues that need to be addressed before this is ready.

Merge readiness

• GitHub mergeStateStatus is BLOCKED (review requirements), not a conflict: mergeable: true, merge-base and live main are both 99721c762f37cd43ac511007a5f51d1846df959e, and all required CI checks on head 94c90879fdeffd424472ee46f911e260af19b8bc are green.
• I re-checked my earlier CHANGES_REQUESTED review on dc3ec651 (late fork after plan, parent-bearing Create, continuation after metadata removal). On this head those look addressed: TestPruneKeepsAParentForkedAfterThePlan, TestContinuingASessionPruneIsRemovingIsRefused, and the related CLI/ACP/TUI tests pass locally on Linux.
• CodeRabbit Docstring Coverage warning (~47% vs 80% on touched functions) is merge-readiness noise unless we treat it as a required gate.
• Superseded attempt #982 (closed); #1091 is daemon capacity, not overlapping scope.
• ACP refreshSessionHistory + load: On existed == true, refresh can treat ErrPruning as a load warning while resume hard-fails. That is a narrow race (first loadHistory already succeeded); session/load while prune holds the lease is refused on the first path (TestACPLoadAndResumeAreRefusedWhilePruneHoldsTheSession). Load’s deliberate best-effort policy (activatePersistedSession ~297–300) may cover refresh. I am not raising it as a finding after a drift pass; optional hardening if we want ErrPruning carved out on refresh for load too.

Findings

🟡 P2 — Dry-run must apply the same removal-time decisions as a real prune

📍 Where: internal/sessions/prune.go (Prune dry-run branch ~175–177 vs pruneSession ~272–325), internal/cli/sessions_prune.go (report formatting), internal/cli/sessions.go (help ~574–578).

💥 What fails: With DryRun: true, the removal loop appends candidates straight to Removed and never runs pruneSession. Removal-time gates—including childCreatedAfterPlan (post-plan fork/child), the second exclusive lease check, write-lock age recheck (PruneKeptUpdated), and open-at-removal handling—only run in pruneSession. Example: TestPruneKeepsAParentForkedAfterThePlan forks a parent in prunePlannedSeam; a real run keeps the parent (PruneKeptParent), but a dry run on the same interleaving lists the parent under “Would remove” because the dry-run branch skips childCreatedAfterPlan. A probe test mirroring that scenario with DryRun: true fails on head 94c90879.

🔎 Root cause: Dry-run reporting is tied to the planning snapshot only. Every removal-time rule in pruneSession (including the post-plan child scan you added for the late-fork case I asked for) is omitted from the dry-run path, so operator-facing dry-run/JSON output can disagree with a subsequent real run on the same disk state.

📜 Stated contract:

DryRun decides everything a real run would and removes nothing. — internal/sessions/prune.go (PruneOptions)

--dry-run List what prune would remove, and why it keeps the rest — internal/cli/sessions.go (writeSessionsHelp)

🏷️ Attribution: PR-introduced. Merge-base has no prune command; this head documents parity but implements dry-run without pruneSession’s removal-time decisions.

📌 In this PR:

• prune.go — dry-run loop vs pruneSession / childCreatedAfterPlan
• sessions_prune.go — text/JSON report surfaces dry-run Removed/Kept
• sessions.go help — dry-run parity claim
• prune_test.go — TestPruneDryRunDecidesTheSameAndRemovesNothing covers static old sessions only; no dry-run case for post-plan fork (unlike TestPruneKeepsAParentForkedAfterThePlan)

🔒 Unchanged on main: N/A (new command).

🔧 Required correction: Share one decision path between dry-run and real removal (evaluate keep/remove reasons without deleting, or run the same helper pruneSession uses for gates). Dry-run and JSON output must list the same Removed/Kept reasons a real run would, including post-plan children and removal-time rechecks. Add regression coverage mirroring TestPruneKeepsAParentForkedAfterThePlan with DryRun: true (and at least one removal-time recheck case).

🛠️ Author fix: Close dry-run parity on every in-diff row above in one pass—do not patch only the dry-run append site without updating help/tests. Do not change real-run deletion order or lease design.

🚫 Out of scope: Redesigning planning, changing the 24h floor, or rewriting unrelated session list APIs.

[jatmn]

lgtm

[Vasanthdev2004]

@jatmn thanks for re-approving. For the record, you were right about the dry run: it appended every planned session to Removed without calling pruneSession, so none of the checks made once a session is held for removal ran. Fixed in ff04d2fc: pruneSession takes the dry-run flag, makes each of those checks under the same locks (the second lease check, the re-read of the last update, the look for children made after the plan) and stops before removing anything. The removal loop has no dry-run branch any more, so a session a dry run would keep also keeps its ancestors, the same as in a real run.

TestPruneDryRunDecidesLikeARealRunAtRemoval runs three cases both ways from the same start: a fork made after the plan, a write since the plan, and a session opened since the plan. Both reports must be the one a real run gives, and the dry run must leave every session's metadata in place. Putting the old short-circuit back fails all three on the dry-run leg (removed [parent] kept [] for the fork). So does moving the dry-run stop above each check in turn, or below the metadata removal. Those are rows D1 to D5 in the description.

A dry run can now fail to check a session, so the text report heads those Could not check rather than Could not remove, which read oddly above "Dry run: nothing was removed." That's D6.

On the ACP refresh note, I'm leaving it as it is. By the time refreshSessionHistory runs, the first loadHistory of the same activation has taken the session's lease on the same store, and the store keeps it for the life of the process. So prune can't be holding the session then, and a second HoldToContinue on a session the store already holds doesn't contend. A quick check: after one HoldToContinue, a prune from another store keeps the session as open in another Zero process, and the second HoldToContinue returns nil.