research: unify session operation addressing

[ctgowrie]

Description

Closes #1580.

Proposes one aligned session-operation model across dynamic channel addresses and fixed durable session IDs.

The proposal is authoring-first and covers:

• custom-channel from(address) sources for dynamic send/respond/control operations
• top-level resolveSession(address) beside from(address) for explicit dynamic-to-fixed snapshots
• internal-only generic address handles, with no public ChannelAddress authoring API
• fixed Session and client handles for exact-ID operations that never create or follow replacements
• positional session.send(message, options) and session.respond(inputResponses, options)
• object inputs for client and eval sends, while eval start(message) stays positional
• cross-channel and schedule to(channel, target).send(message, options)
• flat Slack ctx.send(message, options) and ctx.respond(inputResponses, options)
• the preserved Chat SDK bridge API: send(input, { thread, ... })
• channel lifecycle identity through ctx.session.id, with session.failed.data.sessionId outside session context
• singular, session-ID-only eve HTTP routes with follow-up delivery at POST /eve/v1/session/:sessionId
• JavaScript client, eval, TUI, runtime, race, and removal semantics

Related: #942, #216, #671.

How did you test your changes?

• pnpm exec oxfmt research/session-operations/unified-session-operations-proposal.md
• git diff --check
• verified the required research frontmatter and final implementation shapes

No package tests or changeset are needed because this PR contains only the proposal document.

PR Checklist

• I linked an issue with prior discussion confirming this change is wanted
• I ran the relevant checks from CONTRIBUTING.md
• I added tests and documentation where relevant
• I added a changeset if this touches the published eve package (not applicable)
• DCO sign-off passes for every commit (git commit --signoff)

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